Shadows are a phenomena known in lighting caused by uneven or unbalanced lighting. It can occur in both indoor and outdoor lighting applications.
Shadowing occurs when the light between fixtures is noticeably not as bright than the light under a fixture. It can occur with as little as a 5 foot candle drop from brightest to least brightest within a given space. Light is usually brightest right underneath the fixture and the least brightest in the center point between fixtures. If the light levels drop off significantly between these locations, it appears as if a shadow is creating the darker areas. This effect is also known as “tunneling”.
This phenomena is more noticeable is lower ceiling installations. It is harder to produce wide beam spreads in lower ceiling height areas. Long interior office hallways lit by recessed cans are a good example of tunneling. Under the light, the area is well lit. And then as you walk away from the light, it is significantly darker, and then starts to get brighter once you get closer to the next light.
Creating a bright safe environment is desirable. You will notice shadowing in a space, and it will provide a sense that something is off, or wrong. Bright even lighting does not provide this negative experience.
A Room with Shadows
A Room with Balanced, Even Lighting
What Causes Lighting Shadows?
There are several things that can cause shadowing. Some are obvious. Here’s a list of the top 4 reasons shadows are created.
1. Lights are installed too far apart
If the distance between lights is too far apart, then the light does not have a chance to get to all the areas in between the lights. This problem is exasperated in low ceiling height applications.
2. Using fewer brighter lights to save on installation costs
Sometime facility owners will try to save money by using fewer “more powerful” lights than using more “less powerful” lights. The former will cause shadowing, creating brighter spot lighting under the fixtures with more noticeable dark spaces in between fixture mountings.
3. Obstructions in the way of the light
It could be machinery, tall shelving, walls or even trusses that hang down below the natural path of the light. The more obstructions that get in the way, the more likely you will see shadowing and dark spaces.
4. Using “tight” optics when a wider beam is needed
One of the features that LED Lights offer is the ability to select a beam angle. The higher the number, the wider the dispersion. It is common to use narrower beam angles at higher mounting heights and wider beam angles at lower mounting heights. Shadowing occurs when the wrong beam angle is used.
The Path to Success: Lighting Plans
A lighting plan is a report generated by sophisticated lighting software. It provides details of the space that include
average foot candle levels (or lux levels)
type of fixture used
number of fixtures used
location of fixtures
mounting height of fixture
average / minimum ratio between average foot candles / minimum foot candles
What does average to minimum ratio mean?
The lighting plan to the right is an example of one of the pages we create when doing a customer lighting plan. The average / minimum ratio is the number to pay attention to when determining if the light is balanced or not. Lower numbers are better. A average / minimum ratio between 1.5 and 3.0 is a good indication that the light levels in the space are even and balanced.
Average to minimum doesn’t always tell the entire picture
However, there are times when this number creeps higher and the light in the main space is still considered balanced.
The corners of any space will always be the darkest. If you eliminate the four corner foot candle calculations, it will give you a better representation of lighting across 99+% of the space. So there are times when we will eliminate the corner calculations in a lighting plan to ensure the corners are not skewing the true representation of the majority of the space.
Where Lighting Plans Fail
There are times when lighting plans will fail. And its not the fault of the lighting plan.
Not understanding the physical limitations of the room could affect the results. For example, if there are obstructions that are not communicated to the lighting plan designer, they will develop the plan thinking the space is wide open.
The second, and probably the biggest issue we’ve seen, is swapping out the light from the one modeled in the lighting plan. This is almost as bad as not doing a lighting plan at all. The lighting plan is designed specifically for the chosen lights. You should expect great results if you follow the lighting plan and use the selected fixture. However, swapping out the fixture is more likely than not a recipe for failure. We say this because we have seen this happen. A customer asks us to produce a lighting plan, and then they swap out the lights with something they found on a clearance site, and the results are terrible.
The Cost Free Formula for Success
It’s really simple. Do a lighting plan. Provide all the information you can. Discuss any obstruction that might be in the way. And let us generate a cost free lighting plan for you ( we provide these free of charge for Electrical Contractors, Escos, or commercial and industrial end-user customers. Lighting plans are generally not free. They can cost upwards of $500-$1000 to do. But we know that when we do one, the results always turn out properly. The light levels are what the customer wants and needs, and we have eliminated all shadows and un-even lighting.
About the Author
Dwayne Kula is President of LED Lighting Supply. On any given day, Dwayne is writing content for the site and helps manage the marketing initiatives that are on-going. He has a Software Engineering degree and still dabbles in writing software for the company as needed. When not working, he enjoys spending time with his family, working out, playing the occasional game of golf and exploring New England.